What Is Myasthenia Gravis?

Medically reviewed by Nicholas R. Metrus, MD

Myasthenia gravis (MG) is a chronic (long-term) autoimmune disorder that causes muscle weakness and fatigue. When a person has an autoimmune disorder, their immune system attacks healthy cells, tissues, or organs by mistake. With MG, the immune system creates antibodies that change or block the connection between nerves and muscles.

Although myasthenia gravis can affect any muscle, it most commonly affects muscles that connect to your bones (or, skeletal muscles). These muscles support body functions such as breathing and body movement in the arms and legs.

Your healthcare provider will use a combination of blood, nerve, muscle, and imaging tests to make an MG diagnosis. Currently, there is no known cure for myasthenia gravis, but treatments help reduce symptoms and minimize possible side effects from medications.

Myasthenia Gravis Symptoms

Myasthenia gravis causes weakness in the skeletal muscles. This muscle weakness usually worsens after activity and improves after periods of rest. Although the condition can affect any muscle, it most commonly affects muscles that control the following:

• Eye and eyelid movement

• Facial expressions

• Talking

• Chewing and swallowing

The onset (or, start) of MG can often be sudden. People experience different levels of muscle weakness. Other symptoms of myasthenia gravis include:

• Weakness in the arms, hands, fingers, legs, and neck

• Drooping of one or both eyelids (ptosis)

• Trouble talking

• Blurred or double vision

• Feeling like you are not getting enough air or shortness of breath

• Trouble swallowing

Types

Muscle weakness and fatigue can be localized (affecting specific muscles) or affect multiple muscles. Myasthenia gravis is classified as generalized or ocular. Transient neonatal is a temporary form of MG that affects newborns.

Generalized Myasthenia Gravis

Generalized myasthenia gravis describes symptoms that affect multiple muscle groups. This type of MG typically affects:

• Muscles in the eyes, face, jaw, and throat area

• Arms and legs muscles

• Muscles involved in breathing (respiratory muscles)

Ocular Myasthenia Gravis

Ocular myasthenia gravis describes symptoms that are limited only to your eye muscles. Symptoms of ocular myasthenia gravis are mistaken for a stroke in the brainstem or nerves that control eye movements. Graves' disease (another autoimmune condition) is often misdiagnosed as ocular MG.

Transient Neonatal Myasthenia Gravis

Transient neonatal myasthenia gravis occurs in babies born to mothers with the condition. Newborns develop this temporary form of MG 48 hours after birth. In addition to muscles weakness, newborns experience symptoms such as:

• Impaired sucking or swallowing

• A weak cry

• Low muscle tone (hypotonia)

• Little spontaneous movement

These symptoms may last for days to weeks. After some time, infants gain normal muscle strength.

What Causes Myasthenia Gravis?

Myasthenia gravis is an autoimmune condition that affects the nerve-muscle junction—where nerve endings connect with muscles. The immune system creates antibodies that block the flow of nerve signals to muscles. This leads to hallmark MG symptoms such as decreased muscle movement and muscle weakness.

Anti-Acetylcholine Receptor Antibodies

When the immune system functions normally, it makes antibodies that bind to harmful germs and mark them for destruction. The immune system uses this process to protect the body from harmful substances like toxins, bacteria, or viruses.

In myasthenia gravis, the immune system makes antibodies that block, alter, or destroy receptors for acetylcholine—a chemical that nerve cells use to communicate. When electric signals travel through a motor nerve, the nerve releases acetylcholine which binds to acetylcholine receptors on muscle fibers. This causes muscles to contract.

Antibodies that block, alter, or destroy receptors for acetylcholine are called anti-acetylcholine receptor antibodies (anti-AChR). As the anti-acetylcholine receptor antibodies continue to destroy acetylcholine receptors, the number of receptors decreases.

As a result, signaling between nerves and muscles doesn’t work as well and leads to weaker muscle contractions. This leads to MG symptoms, including decreased muscle movement and weakness.

Anti-MuSK Antibodies

Some people with anti-AChR also have antibodies that attack another protein called muscle-specific kinase (MuSK). The presence of anti-MuSK antibodies also decreases the number of acetylcholine receptors.

Overactive Thymus Gland

The exact cause of myasthenia gravis needs to be better understood. However, research shows that about 75% of people with MG have an abnormally large and overactive thymus gland (an organ that controls immune function).

Researchers suspect the thymus gland may send incorrect instructions to developing immune cells. This causes the immune system to malfunction and produce acetylcholine receptor antibodies.

Diagnosis

Myasthenia gravis can be hard to diagnose because its symptoms are similar to other health conditions. In addition to taking your medical history, your healthcare provider (usually a neurologist, or a doctor who specializes in the brain and spinal cord) may order any of the following tests to make a diagnosis:

• Neurological exam: An exam to check your reflexes, muscle strength and tone, coordination, balance, sense of touch, and sight.

• Ice pack test: An ice pack is placed on a droopy eyelid. If drooping improves, it may mean you have MG.

• Antibody test: A blood test to look for acetylcholine receptor antibodies and anti-MuSK antibodies. Some people with myasthenia gravis have neither of these antibodies.

• Electromyography (EMG): Electrical signals to the muscles are measured when muscles are at rest and being used.

• Nerve conduction study: This test measures how fast and how well electrical signals travel through your nerves.

• Imaging tests: A computerized tomography (CT) scan or magnetic resonance imaging (MRI) may be used to check if you have an enlarged thymus or a thymus tumor.

• Edrophonium test: Edrophonium is a drug that relieves muscle weakness related to MG. If muscle weakness improves after receiving edrophonium, you may have MG.

• Lung function tests: These tests measure breathing and how well your lungs are working.

Getting a diagnosis can be a stressful and long process. It is common for a myasthenia gravis diagnosis to be delayed or even missed. Some people with milder muscle weakness symptoms may experience a delay of up to two years. If you are concerned about an autoimmune diagnosis such as myasthenia diagnosis, take steps to advocate your care, such as:

• Keep a record of your symptoms.

• Know your family history of myasthenia gravis and other autoimmune conditions.

• See a specialist who has experience with your most major symptoms.

• Consider seeking a second or third opinion if your primary healthcare provider dismisses your symptoms.

Complications

A myasthenic crisis is a sudden and severe weakness of the jaw, throat, or respiratory (breathing) muscles. A crisis can be triggered by infections, severe stress, or surgery. It affects about 10% of people living with myasthenia gravis.

During a myasthenic crisis, this muscle weakness blocks the upper airways, making it hard or impossible to breathe properly without help. A myasthenic crisis is a medical emergency that requires breathing assistance in the form of ventilation.

Treatments for Myasthenia Gravis

There is no known cure for myasthenia gravis, but it is a treatable condition. The goal of treatment is to reduce symptoms and minimize possible side effects from medications.

A treatment plan will be created based on the severity of your symptoms, which muscles are affected, and your medical history. A combination of therapies may be used as part of your care. Your healthcare provider will monitor your response to treatment and adjust your treatment plan as needed.

Symptomatic Treatment

Initial treatment for myasthenia gravis starts with cholinesterase inhibitors. This medication prevents the breakdown of acetylcholine, decreasing symptoms of muscle weakness. Mestinon (pyridostigmine) is a cholinesterase inhibitor used to treat MG.

Immunosuppressive Treatment

If your myasthenia symptoms are still active after taking Mestinon, your healthcare provider may prescribe immunosuppressive treatment. Immunosuppressive medications help reduce immune system activity.

First-line immunosuppressive medications include steroids such as prednisone and Imuran (azathioprine). If you are unable to take first-line drugs, the following second-line drugs are available:

• Otrexup or Trexall (methotrexate)

• Cellcept or Myfortic (mycophenolate mofetil)

• Astagraf XL, Envarsus XR, and Prograf (tacrolimus)

• Gengraf or Neoral (cyclosporine)

Intravenous Immunoglobulins (IVIG)/Plasmapheresis

Intravenous immunoglobulins (IVIG) and plasmapheresis work quickly and offer short-term relief for a few weeks. These therapies may also be used:

• Treatment for a myasthenic crisis

• Before surgery

• If your symptoms are not responding to immunosuppressive treatment

IVIG helps prevent the immune system from further damaging the nerve-muscle junction for a short period of time. Soliris (eculizumab) is an IVIG medication available as an intravenous infusion.

Plasmapheresis (or, plasma exchange) is a process in which anti-AChR is filtered from the blood. This lowers the amount of anti-AChR which. This allows for relief from severe myasthenia gravis symptoms.

Surgery

For a small number of people, myasthenia gravis may be due to a tumor in the thymus (or, thymoma). In these cases, removal of the tumor and the remaining thymus (thymectomy) is recommended. Unless a thymoma is present, thymectomy is not recommended for people with ocular MG.

Most people who get a thymectomy see an improvement in their MG symptoms.

Living With Myasthenia Gravis

Most people living with myasthenia gravis can live a normal life with proper treatment. In the past, myasthenic crises were a major cause of death. With improved treatment and care, the mortality rate for myasthenic crisis reduced to 4.47% (previously it was over 50%). Research has led to fewer delayed and more accurate diagnoses.

If you are living with MG, there are steps you can take to improve your daily life with the condition. This includes the following:

• Avoid medications that worsen MG symptoms: Talk to your healthcare provider and pharmacist when starting any new medications.

• Triggers: Learn about what triggers your MG symptoms and how to avoid them best.

• Routine vaccinations: To help reduce your risk of myasthenic crisis and respiratory issues, stay updated on your flu and pneumococcal vaccines.

• Ease fatigue: Budget your energy throughout the day and get plenty of rest.

• Wear a medical identification bracelet: This can alert paramedics that you have myasthenia gravis in case of emergency.
  

Frequently Asked Questions

Can COVID trigger myasthenia gravis?

Yes, infections such as COVID-19 can trigger myasthenia gravis symptoms or a myasthenic crisis.

Is myasthenia gravis a form of multiple sclerosis?

Although both are autoimmune diseases, myasthenia gravis is not a form of multiple sclerosis.

Does vitamin D help myasthenia gravis?

Although more research is needed, studies have shown that supplementing vitamin D can help reduce myasthenia gravis fatigue symptoms.

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